“Do-it-yourself” Septic System Design
Having trouble with your Septic System? Can’t take a shower and run the washing machine at the same time without having to clean-up a system back-up? You have a nice wet green area in your yard when the rest of the lawn is brown? Do you think it is time to replace the old Septic System?
Why not “do it yourself”?
While some of the following information could apply to other States, the focus of this Blog is to address residential septic systems in Massachusetts.
The first step is to understand what is a Septic System, which is also known as an on-site sanitary wastewater disposal system. The Massachusetts Department of Environmental Protection (MA DEP) maintains a website with lots of information. The trick is navigating through the site (link to the main DEP Septic System page) to find the answers you need. In Massachusetts, the design of septic systems is controlled by the State Sanitary Code (310 CMR 15.00) which is also known as Title 5 which can be obtained at this MA DEP Septic Systems/Title 5 link . Each community can also establish local regulations that have to be followed. You should check with the local Board of Health office.
Before you get started using the Code to do the design, let’s become familiar with the basic septic system components.
Sanitary wastewater leaves the house through the building sewer and flows by gravity into the Septic Tank. In some instances, the design requires a pump to move the septic tank effluent to the leaching system (also know as the soil absorption system or SAS)
The effluent leaving the septic tank and/or pump chamber has to be piped to a Distribution Box (“D” Box) before entering the SAS. The Distribution Box is designed to allow the effluent to be distributed evenly into the leaching system by gravity (there are pressure dosed systems that do not use a “D” box).
Distribution boxes are typically made of concrete and are available with multiple pipe openings and sizes.
The SAS or “leaching area” allows the distributed effluent to pass into the ground.
There are multiple types of systems and components that have been approved for general use in the design of this system component. The decision to use a pipe and stone leaching field, pipe and stone leaching trench, chamber system or other type of system should be based on the specific site conditions and property constraints.
The MA DEP web site also published a series of technical design documents that are available at this Guidance and Policy link.
Now that you are more familiar with the systems components and have copies of the regulations, there are a few more steps that need to be accomplished before you can work on the design. You will need to prepare a plan of your property to show the existing house as well as the site features, such as the driveway, trees, swimming pool, etc. This plan needs to show your property line (your deed will describe your property and may even reference a plan that shows your lot lines). This plan also needs to show topography (your town may require the topography to be based on a national datum and not an assumed elevation) and spot elevations at certain locations. It is also helpful to know the location and invert elevation of the building sewer pipe at foundation as well as the location of your water service and other utilities (gas, electric, CATV). If you or your neighbors have a well (drinking water and or irrigation well), then they (all the wells) also need to be located and shown on the plan.
Do you have wetlands within 100 feet of your property or where the new septic system would be installed? Then you will need to have the edge of the wetlands determined, located and shown on the plan. Some towns have local Wetlands By-laws & Regulations which are more stringent that the State Regulations, so it may be best to contact your local Conservation Commission office.
Now that you have your worksheet plan, you can determine what area is available to locate the new septic system. The Code has a list of set-back distances that need to be followed, such as 10 ft. off the property line, etc.
The next step will require the services of a MA licensed Soil Evaluator to perform the official soil evaluation and percolation testing. This testing is witnessed by the local Board of Health and typically involves submitting an application along with a fee payment. The testing will involve the excavation of several deep (10 ft. plus) holes in the proposed system location, so you will need a larger backhoe. You (or your excavating contractor) will need to obtain a “dig-safe” number and a Trench Permit (issued by the town).
The soil evaluation will determine the depth and suitability of the soil, the elevation of the estimated seasonal high groundwater and the percolation rate. These items are all used in determining the elevation of the system components as well as the size of the SAS.
If you have a property that has high groundwater and the good soils are saturated (can’t perform the percolation test), then a soil sample can be taken to a State Certified Soils Lab to perform an analysis to determine the classification for establishing a percolation rate. This is only allowed for system replacement when no increase in flow is proposed.
Speaking of flow, the Code requires you to use a design flow based on the total number of bedrooms. If you have a house with more than 10 rooms, you are required to do a mathematical calculation to arrive at the bedroom count. The Code uses 110 gallons per day per bedroom with a three bedroom minimum design. Some towns require a higher design flow amount.
Now you can take all of this information and do the design for your septic system! The Code has a listing of all the items that must be presented on the design plan and some towns have additional content requirements.
In Massachusetts, the final design plans that are submitted to the Board of Health for approval must be prepared by a Registered Sanitarian or a Registered Professional Engineer.
Maybe the “do-it-yourself” method is not a good idea.
However, by knowing what is involved with this process and the multiple options for replacing a failed septic system, you can use this knowledge in hiring the Sanitarian or Professional Engineer who will work closely with you in preparing a final plan that is best suited for your property.